The 19-year-old French centre-back says that the Portuguese is "like a second father" to him and has helped him develop his game.
"Jose Mourinho is like a second father to me," Varane told French TV channel TF1. "In football terms, he has significant input.
"He shows his support and his faith in me. He finds the right words to give you the peace of mind to be able to improve, which is important. We often talk. He's really close to his players."
Varane joined Madrid from Lens in 2011.